There are sites that mirroring file to several file sharing/storage sites. Example:
https://www.mirrorcreator.com/
http://www.uploadmagnet.com/
But file sharing sites delete file within some days (30,60..)

Is there any way to automatize re-uploading of the files so they do not die?

I think this can be done, but re-uploading would need webserver to be able to download file from one of the old file sharing servers, but there is captcha usually.

Or any other way to keep file online?
I see torrent with DHT, Tribbler maybe, but are there any other ways?